Dog Vomit Slime Mold, (Physarum polycephalum)

The first slime mold I saw frightened me. It was growing on a tree stump in our front yard, and I was at that time taking a course in fungal diseases. It really is harmless. It decomposes vegetable matter. The name is a good description of this weird organism. Although it looks like a mold, and it releases spores like a fungus, it moves. Slime molds are currently classified with the Protista, single-celled organisms like the amoeba or paramecium. But unlike them, it has a complicated life history which includes a colonial stage. One stage of its life begins as a spore: single-celled with only 1 set of chromosomes. When ripe, the spore can either become amoeba-like, and move by bulging itself in a direction with the rest of the cell contents flowing behind (streaming). Or, it can grow a flagella, a moveable “tail” which can propel it forward. These swarm cells move about, ingesting the bacteria they encounter. When food is scarce, if it meets another swarm cell of like kind (amoeboid or flagellated), the two will fuse together. They now have a paired set of chromosomes. This new creation then duplicates all chromosomes, again and again, and becomes a multi-nucleated organism within a single cell membrane. This is the stage we encounter, usually on a rotting log or tree. It is now called a plasmodium, and it too can stream about like a very large amoeba, flowing over the surface as it seeks dead vegetation, bacteria, yeasts, and fungi. It can sense air-born chemicals, and direct its flow toward the source. It surrounds its food, and secretes enzymes to digest it, and then ingests the components. Slime molds prefer damp shady areas with lots of organic matter. It tries to avoid light. However, if it is exposed to light, or if food gets scarce, the plasmodium can quickly change into a fruiting body. Stalks arise from its surface, bearing spores. When released, these spores can be spread by the wind. Spores can also remain dormant for years, until favorable conditions allow it to become a swarm cell. The spores absorb moisture in cool humid conditions, split and escape from the spore coat. The life-cycle now repeats itself. DNA research has shed a light on the relationships of slime molds and their evolutionary history. They seem to be very ancient organisms, perhaps a billion years old, and may have been the first life to live on land, rather than in the oceans. It also seems, perhaps, to have a form of intelligence. Research has claimed that P. polycephalum can find the shortest route through a maze when food was placed at the exit. The amoeba also makes a pattern of networks between several food sources, and cycles between them to achieve a balanced diet of protein and carbohydrate. Further research will show whether these claims are true. Regardless, Dog Vomit is an interesting organism. Article by Eve Broughton. Eve lives in Whitethorn and was educated at UC Berkeley.  ]]>